1. Field of the Invention
This invention relates to a process for producing carbon material which can be used either in the form of fibers or various molded articles as fillers for various composite materials, heat insulating materials and ablation materials, or in the form of activated carbon materials including molecular sieve carbon materials, activated carbon fibers and the like as adsorbent or separating materials.
2. Description of the Related Art
Among carbon materials in such fibrous forms as generally called carbon fibers, molecular sieve carbon fibers or activated carbon fibers, carbon fibers are produced by spinning rayon, lignin, polyacrylonitrile (hereinafter referred to as PAN), pitch or the like, rendering the spun fiber infusible, carbonizing it at a temperature of 1,000.degree. to 1,600.degree. C,,or further graphitizing the resulting carbon fiber at a temperature of 2,000.degree. to 3,000.degree. C. On the other hand, molecular sieve carbon fibers and activated carbon fibers are produced either by spinning a raw material as described above, rendering the spun fiber infusible, and then activating it, or by rendering the spun fiber infusible, carbonizing it, and then activating the resulting carbon fiber.
Although these carbon materials in fibrous form have excellent properties which are not possessed by other materials, they involve several operational problems as described in the following paragraphs (1) to (3). Therefore, these carbon materials are high in price and still far from being widely used as common industrial materials.
(1) In order to provide industrially practicable spinnability, the spinning material must previously be freed of any foreign matter by high-precision filtration. PA1 (2) Rayon and PAN are spun according to the wet or dry spinning technique, which involves the cost of solvent recovery. On the other hand, the spinning of lignin and pitch produces tar and mist, so that it is important to control the spinning atmosphere. PA1 (3) All of the fibers spun from the aforesaid raw materials require a treatment for rendering them infusible. Generally, this treatment is carried out by air oxidation. In this treatment, a long treating time, large-capacity oxidizing equipment and the like are needed to prevent violent exothermic reaction, i.e., combustion.
In order to eliminate the time-consuming step of rendering the spun fiber infusible by air oxidation, there has been proposed a process in which fibrous polystyrene is soaked in sulfuric acid and then carbonized (Japanese Patent Publication No. 36085/'86). However, this process has the disadvantage that the sulfonation of polystyrene (i.e., the introduction of sulfonic groups into polystyrene) is not effected uniformly throughout the entire fiber. That is, spots rendered infusible, spots made fragile due to excessive sulfonation, and spots not rendered infusible are formed in the fiber surfaces, resulting in a very inhomogeneous fiber.